How to blend(gradient effect) two different 3D materials, in cycles blender
Final result:



Overview:

You can use Gradient Texture as a mask for your textures.

Prepare you textures as usual with needed normals/bumps and mix them trough Gradient Texture or which ever you need.



Edit:

If you are using Image Textures don't forget you need proper Texture Coordinates no matter if they are form UV mapping or using Generated/Object texture space.

Blend file: